Science

Botony Brown – Why Do the Leaves Fall From the Trees

January 26, 2017
Decrepit Leaf

“All the leaves are brown, all the leaves are browwwwn, and the sky is grey and the sky is greyyyyyy…”

That song by The Mamas and the Papas popped into my mind the other day thanks to an inquiry that came hurtling up to the dashboard from the back of the van.  This actually happens quite often – not the song invading my head, but the question launching that occurs while I am driving.

In addition to the seven year-old, who is in large part responsible for this journey after he fearlessly inquired when I was returning to school to relearn things, I also have five year-old boy/girl twins.  The inquiry came from one of them.

I will not go into great detail about the brain power loss they are responsible for.  I will say this:  I am missing about 15 months of memory, in addition to some amount of information I am sure was housed in my noodle, which is now unaccounted for and not remembered anyway so can’t be accounted!  It is so confusing.

Anyhow, we were driving home from pre-school the other day through our lovely neighborhood where the landscapers come along with their leaf-blowers in-mass and pile up the leaves from the sidewalks and green areas and heap them alongside the road to be whisked away like we live in Pleasantville or The Truman Show.  Today the leaf-sucker truck, as I like to call it, was there sucking up the collective piles of leaves as we drove through.

Some might call it a leaf-vacuum truck.

Not me.  To me it is the ‘leaf-sucker truck.’  This is exciting.  I love, love, love the leaf-sucker truck, so of course I look in the rear view mirror at the kids and exclaim,

“Look guys!  There is the leaf-sucker truck sucking up the leaves!”

Pretty simple statement of an innocent and simple observation made by mama brain. Well, mama brain expected a few “ooos” and “ahhhs” or maybe even a bold, “SLOW DOWN!” and then fa-la-la-la-la-la-la-la-la back to the Christmas songs on the radio.

Well, apparently that was just the kindling for what followed to challenge my knowledge stores, or lack there-of. It started with an expression from my youngest child (by one minute) about how the leaf-sucker truck is not liked by him because it is taking the pretty leaves away.

Well, that is sad, but…okay, so we live in North Carolina where the leaves fall a wee bit later than some other parts of the country and boy are they pretty, but it was almost Christmas day.  These leaves are lifeless, decrepit, ugly-brown, crackling on the ground and crumbling under the blink of an eyelash.

hand and leaf

If the trees are not naked, they are hoarding brown carnage for some unknown biological reason and surely impairing their abilities to survive the winter, due to their inability to let it go.  Surely, they have heard that screeching song from the insides of cars zooming by sung by little snow princesses?

Anyway, I explained how the leaf-sucker truck is sucking up all of the leaves because they are dried up and dead.  The trees don’t need them for food anymore. The colors are gone.  Bam.  Done. Fa-la-la-la-la-…

What came next was some conglomeration of an inquiry about how do the leaves make food for the trees and how do they then fall off of the tree and why does the tree do that and I don’t remember what else.  Silence.  “Shall I put in the Christmas CD our elf brought?!”

I took Botony in college.  Um yeah.  I do not remember much.  In my defense, Botony was more than a few years ago. More than a decade.  Maybe more than two, but who is counting?  Sure, words like xylem and phloem and mitochondria and chlorophyll are still present in my brain, but what purpose they serve for our lovely plants: not-so-much.

As I mentioned, I am driving and like any mama out there I avoid the smart phone while driving, so Google or Bing couldn’t throw me a bone.  Well, my son is five, so I sheepishly said, I am not sure how they make their food and then why the tree rejects them after all the leaf has done to feed the parasite tree for months and months and months while it bakes in the heat and humidity of our sometimes armpit-like summers, or something to that effect.  Exhale.

He took the answer and silence fell in the middle row of the van and we returned to our fa-la-laing.

But I was smacking my head for not being more-equipped with the science behind the trees’ seemingly senseless rejection of the leaves for this young, impressionable mind who also happens to be my offspring.  Scratch Stanford off of the list.

Here is where I took the bull by three horns (don’t ask me why it has three horns).  One: I need to know.  Two:  I need to be able to answer the question without yet another of my children thinking I need to go back to school or that I am some miserable brainless failure, and Three: I need to share it with my lionesses so your offspring don’t think that you are some miserable, brainless failure like me!

The latter of which I am sure would never happen regardless, but a little plant knowledge is good for the soul though.  I mean.  After all, we eat them, so shouldn’t we get to know them a little more?  I think so.

Grab a salad and read on.

What do leaves do and why do they fall from trees?

A leaf’s job is to make food for the plant via a process called photosynthesis.  They use sunlight for energy to take apart water from the ground and carbon dioxide from the air to make sugar to fuel the plant. Water gets to the leaf through xylem, which are tubes and transport cells that circulate water and dissolved minerals.  The phloem then delivers the sugars and other molecules created by the plant. Carbon dioxide (CO2)comes into the leaf through small openings on the bottom of the leaf (stomata), which also release oxygen as a byproduct from using the CO2 and water to make food.  Take a deep breath of that fresh O2!  Thank you trees!

When leaves are making food they use chlorophyll to get energy from the sun, which is green thus making the leaves green.  When the leaf is ready to stop making food because sunlight is less available to energize them and temperatures are cooler they stop making chlorophyll.  Without it, the other chemicals in the leaves can then be seen, which are the spectacular colors we see in the fall.  A special layer of cells develops and severs the tissues that support the leaf.  The tree seals the cut and leaves behind a leaf scar.  The leaf falls and then lays lifeless like roadkill on the side of the road, or in your yard/in your gutter to hopefully eventually be sucked up by none other than the leaf-sucker truck!

There are some trees that do not lose their foliage of course.  Those who do suffer the immeasurable loss every fall and leave you holding a rake are called deciduous and those who do not are called evergreen.  Trees are also perennial (they stay alive, unless you kill them, year after year) vs. annual (stay alive for just one season) like pansies, petunias, lantana, etc.

There you have it. Now, I think it’s time for a walk through the woods with my kiddos to explain the carnage on the forest floor, since the suburban leaves have been whisked away by my great friend the leaf-sucker truck.

Journey on!

You Might Also Like